1. Field of the Invention
The present invention relates to a motor-cooling structure of a front-and-rear-wheel-drive vehicle having an engine adapted to drive first driven wheels and a motor adapted to drive second driven wheels, wherein a driving force of the motor is transmitted to the second driven wheels through a reduction unit and a differential.
2. Description of the Related Art
A hybrid vehicle is disclosed in Japanese Patent Application Laid-open Nos. 5-310048 and 6-38303, wherein driven wheels are driven by an engine and/or a motor. A lubricating oil is drawn by a special electric pump and is used to cool the motor.
A hybrid vehicle is disclosed in Japanese Patent Application Laid-open No. 2001-333507, wherein front wheels are driven by an engine, rear wheels are driven by a motor, and a generator driven by the engine is cooled by engine cooling water.
However, in the hybrid vehicle disclosed in Japanese Patent Application Laid-open Nos. 5-310048 and 6-38303, the motor is cooled by drawing lubricating oil using the special electric pump, which results in a drawback as the number of parts is increased due to the required electric pump. While it is conceivable that the electric pump could be eliminated and the motor cooled using oil from an oil sump by a gear, such an approach would have difficulty effectively cooling the motor.
Furthermore, it is also conceivable that the motor can be cooled using engine cooling water as disclosed in the hybrid vehicle described in Japanese Patent Application Laid-open No. 2001-333507. However, such an approach renders bringing the cooling water into direct contact with a rotor and a stator of the motor very difficult, if not impossible. Additionally, the cooling water can be only caused to flow through a housing of the motor. As such, it is also difficult to achieve a sufficient cooling effect.